The overall goal of the proposed research is the elucidation of the geometrical and electronic structures of the active sites of metalloproteins. The principal techniques to be employed involve optical spectroscopy using polarized light and (in part) magnetic fields, specifically circular dichroism (CD) and magnetic circular dichroism (MCD). We also propose to develop new instrumentation and theory for the study of magnetic linear dichroism (MLD). Selected metalloproteins will be studied by CD, MCD and MLD over wide ranges of temperatures, magnetic fields and wavelengths, respectively 1.2-300degreesK, 0-7 Tesla and 180-5000 nm. Spectra of a specific metalloprotein will be obtained in all accesible redox states. Spectra will then be analysed in order to determine as far as possible the nature of the metal-containing prosthetic groups of the proteins under study. Specific metalloproteins to be studied include the iron-sulfur (Fe-S) proteins: Desulfovibrio vulgaris hydrogenase, Klebsiella pneumoniae pyruvate-flavodoxin oxidoreductase, and Micrococcus aerogenes ferredoxin and the nickel-iron-sulfur enzyme: Azotobacter vinelandii hydrogenase. In all cases these metalloproteins are "complex" possessing multiple metal-containing prosthetic groups in the enzymatically active states of the proteins. In the case of M. aerogenes ferredoxin, we will study the oxidative and degradative chemistry induced by Fe(CN)3,6- and similar oxidants. The metalloproteins to be studied are prototypical of classes of enzymes increasingly found in all types of living systems. They are involved in crucial physiological processes. The understanding of these and related enzymes at the chemical level is fundamental to the complete understanding of the workings of living cells, and eventually, to our ability to prevent and cure pathological conditions in cells.